Modern communications systems are using increasingly higher frequencies. At high frequencies, communications utilize higher data transmit/receive rates. When steerable array antennas are used in high frequency communications systems, it is desirable for each antenna element to have fast scan capabilities, small size, low cost and reasonable performance. Phase shifters are critical components for meeting those criteria.
Electronic phase shifters are used in many devices to delay the transmission of an electric signal. Waveguide phase shifters have been described in U.S. Pat. Nos. 4,982,171 and 4,654,611. U.S. Pat. No. 4,320,404 discloses a phase shifter using diode switches connected to wire conductors inside a waveguide that are turned on or off to cause a phase shift of the propagating wave. U.S. Pat. Nos. 4,434,409; 4,532,704; 4,818,963; 4,837,528; 5,724,011 and 5,811,830 disclose tuning ferrites, ferromagnetic or ferroelectric slab materials inside waveguides to achieve phase shifting. U.S. Pat. Nos. 4,894,627; 4,789,840 and 4,782,346 disclose devices that use finline structures to build couplers, signal detectors and radiating antennas. These patents either use slab material in a waveguide to construct phase shifters or use finlines for some other application.
Tunable ferroelectric materials are materials whose permittivity (more commonly called dielectric constant) can be varied by varying the strength of an electric field to which the materials are subjected. Even though these materials work in their paraelectric phase above the Curie temperature, they are conveniently called “ferroelectric” because they exhibit spontaneous polarization at temperatures below the Curie temperature. Tunable ferroelectric materials including barium-strontium titanate (BST) or BST composites have been the subject of several patents.
Dielectric materials including barium strontium titanate are disclosed in U.S. Pat. No. 5,312,790 to Sengupta, et al. entitled “Ceramic Ferroelectric Material”; U.S. Pat. No. 5,427,988 to Sengupta, et al. entitled “Ceramic Ferroelectric Composite Material-BSTO-MgO”; U.S. Pat. No. 5,486,491 to Sengupta, et al. entitled “Ceramic Ferroelectric Composite Material-BSTO-ZrO2”; U.S. Pat. No. 5,635,434 to Sengupta, et al. entitled “Ceramic Ferroelectric Composite Material-BSTO-Magnesium Based Compound”; U.S. Pat. No. 5,830,591 to Sengupta, et al. entitled “Multilayered Ferroelectric Composite Waveguides”; U.S. Pat. No. 5,846,893 to Sengupta, et al. entitled “Thin Film Ferroelectric Composites and Method of Making”; U.S. Pat. No. 5,766,697 to Sengupta, et al. entitled “Method of Making Thin Film Composites”; U.S. Pat. No. 5,693,429 to Sengupta, et al. entitled “Electronically Graded Multilayer Ferroelectric Composites”; and U.S. Pat. No. 5,635,433 to Sengupta, entitled “Ceramic Ferroelectric Composite Material-BSTO-ZnO”. These patents are hereby incorporated by reference. Copending, commonly assigned U.S. Pat. No. 6,514,895 to Chiu et al. titled “Electronically Tunable Ceramic Materials Including Tunable Dielectric And Metal Silicate Phases”, filed Jun. 15, 2000, and U.S. Pat. No. 6,744,077 to Sengupta et al. titled “Electronically Tunable Low-Loss Ceramic Materials Including a Tunable Dielectric Phase and Multiple Metal Oxide Phases”, filed Jan. 24, 2001, disclose additional tunable dielectric materials and are also incorporated by reference. The materials shown in these patents exhibit low dielectric loss and high tunability. Tunability is defined as the fractional change in the dielectric constant with applied voltage.
U.S. Pat. Nos. 5,355,104 and 5,724,011 disclose phase shifters that include voltage controllable dielectric materials.
The prior art does not disclose a finline waveguide structure that is used as a tunable phase shifter. There is a need for tunable phase shifters that are relatively simple in structure, low in cost, and can be rapidly controlled.